1. Field of the Invention
The present invention relates to an electronic endoscope, and more specifically relates to a light source apparatus for an electronic endoscope using a plurality of aperture controlling rotary plates.
2. Description of the Prior Art
In conventional electronic endoscopes, in order to provide appropriate light modulation, an endoscope recording apparatus has been proposed in, for example, Japanese Unexamined Patent Publication No. 62-69222. The apparatus disclosed in this publication is provided with a rotary shutter having a rotatable shaft, wherein the distance between the axis of the rotatable shaft and the optical axis of illuminating light emitted from a light source for the endoscope is variable. The rotary shutter is shaped so that a difference in peripheral speed occurs between the radial portions thereof, i.e., the rotary shutter is shaped so that the aperture size varies during rotation of the rotary shutter. Light modulation is carried out by altering the distance between the axis of the rotatable shaft and the optical axis of illuminating light and by utilizing the peripheral speed difference of the rotary shutter.
In Japanese Unexamined Patent Publication No. 62-69222, light modulation can be performed, however, the structure of the rotary shutter is complex. Furthermore, it is necessary to provide a mechanism to vary the distance between the rotary shutter and the optical axis of the light source for the endoscope. Accordingly, the manufacturing cost is high and the manufacturing process is troublesome. Moreover, in order to achieve such a construction, the outer diameter of the rotary shutter must be several times larger than that of the light bundle, thus resulting in an increase in size of the rotary shutter. If the rotary shutter is asymmetrical in shape with respect to the rotation axis thereof in order to vary the aperture, the center of rotation does not align with the center of gravity, so that the rotary shutter tends to lose balance during rotation. Consequently, correct emission of the illuminating light cannot occur, and the rotary shutter and the surrounding members may break.